A tanning unit is what i'm using too as uv source. I bought mine second hand for 15E. Never had any problems with it. For cyanotypes it gives exposures around 9 minutes at 40-50cm
Did you remove the glass in the front of the light (between the bulb and your print)? It is possible that the glass filters out the UV (a lot are sold that way). Try it bare-bulb and report back!
Points to ponder:
*Paper - the paper you're using may not be appropriate to the process. Papers with a lot of buffering agents in them can cause all sorts of problems. Sizing may also be an issue. Papers that are too heavily sized may not allow enough sensitizer to soak in.
*Exposure - Cyanotypes need a lot of exposure. They're not properly exposed until the image starts to reverse a bit. Even in direct sun here in the desert southwest my exposures run anywhere from 10 to 15 minutes (sometimes less depending on the neg). Underexposed prints will essentially wash away (they might look fine for a moment or two but then - woosh, gone).
BTW, are you using a split back printing frame? If not, I'd highly recommend one. It's much easier to check exposure with a split back frame. For my first print of the day I lay my print out (in the frame) and start my stopwatch. I then expose by inspection, checking the progress (and pausing the stopwatch) at several points until it looks "about right". I note the total exposure time and then process the print. Depending on the outcome I may adjust my final printing time up or down as necessary. Additional prints from the same negative that day get exposed using the time I recording during the test (with any adjustments I may have deemed necessary). The procedure is the same (just a bit more lengthy) if I expose in my UV box.
tanning units are a good choice for simple solution
Some talk about the bulbs for alternative processes..
Obviosuly the light/exposure is the issue here. A Halogen light gives very little UV in the wavelengths used in iron based processes. You could easily be looking at exposures of around 1hr or more (depending of lots of diffrent factors of course). In the UK here most likely the easiest ones to get are the 'bug killer' bulbs, BL tubes I've always found to be the best but not as easy to source or as cheap. A lot will depends on what size your printing of course and how much you want to invest. As for using the sun - well I get a exposure of about 10mins when I'm down in SW France, or about 20-30mins here on a sunny day. You just often need to wait a few months for one though!
Another thing is - are you using any sufactant in your recipie? If not I think some of problem is the fact that the cyanotype solution is just 'sitting' on the surface of the paper, therefore VERY easily washed off. One thing I can strongly recommend is a tiny amount of sufactant to help the sensitiser just penatrate into the very top surface of the paper, rather than sit on the surface.
The normal one used is Tween 20 (i.e. Polysorbate 20). I would mix up about a 2% solution and maybe add 1 drop of that per 5-10mls of sensitizer just before coating. It may well also help you with the coating process. If you dont have/cant get any Tween 20 try using the same dilution of photo-flo as it will help break the water tension a bit. It's not so great but it might help you see if this is the issue.
Last edited by Taraxacum; 08-01-2013 at 06:54 AM. Click to view previous post history.
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